1. Field of the Invention
This invention relates to a head-mount image display apparatus which a user wears on the head to see images.
2. Description of the Related Art
The head-mount image display apparatus used for watching images generally comprises a left image display element for displaying an image to be guided to a left eye, a left eyepiece optical system for guiding the left image to the left eye of the user, a right image display element for displaying an image to be guided to a right eye, and a right eyepiece optical system for guiding the right image to the right eye of the user. Various head-mount image display apparatuses are known, among which are: an apparatus having a pupil distance adjusting system and a diopter adjusting system (Jpn. Pat. Appln. KOKAI Publications 5-196898 and 6-123852), an apparatus having a see-through system (Jpn. Pat. Appln. KOKAI Publication 5-268547), an apparatus for improving the image display (Jpn. Pat. Appln. KOKAI Publication 6-133253), and an apparatus reduced in size (Jpn. Pat. Appln. KOKAI Publication 6-334942).
To decrease the size of a head-mount image display apparatus, the optical guide path for image viewing may be shortened. If the optical guide path is shortened, however, some of the image display elements are located near to the user's nose when the user wears the head-mount apparatus. Suppose either eyepiece optical system has at least three optical faces, e.g. a first face facing the eyeball and having a transmission effect, a second face having a reflection effect and having a rear reflecting mirror, and a third face facing an image display element and having the transmission effect. Then, one corner of the eyepiece optical system is so near to the user's nose as to touch the nose in some mounting conditions. As a result, the user feels uncomfortable while wearing the apparatus.
With the conventional method, in order to solve this problem, the eyepiece optical system may be arranged such that the components of the apparatus do not touch the nose of the people whose pupil distance and positional relationship of eyes and nose fall within a predetermined range of normal distribution. If the eyepiece optical system is so designed, however, the head-mount image display apparatus cannot be maximumly reduced in size and thus cannot be compact. Therefore, the conventional apparatus wherein the eyepiece optical system has a part located too near the user's nose when the user wears the apparatus cannot have its size decreased and give the user a comfortable feeling.
In the case where the eyepiece optical system comprises two prisms joined together, the prisms cannot easily be situated with desired precision (.+-.0.1 mm, for example) after the eyepiece optical system is assembled, unless the strict size management is achieved when the prisms are joined.
In order to accomplish the size management of the prisms, it is necessary to provide to at least two planes as reference planes of the size management for each prism. However, when the eyepiece optical system comprises two prisms, a reference plane of the size management is not provided to the prisms in the conventional head-mount image display apparatus. Therefore, the two joined prisms may shift along the joining face, and the eyepiece optical system cannot attain a predetermined precision. The image guided through such an eyepiece optical system may be deformed and difficult to see.